Dissolution Enthalpy and Entropy of Thiourea in Triglycol Solution

www.bacpl.org/j/pcc Physical Chemistry Communications, Volume 1 Issue 1, April 2014

Dissolution Enthalpy and Entropy of Thiourea in Triglycol Solution Wanren Chen1, Hua Li1*, Xiaoshuang Chen2 School of Chemical and Energy Engineering, Zhengzhou University, Zhengzhou, China, 450001 School of Energy and Power Engineering, Xiʹan Jiaotong University, Xiʹan, Shaanxi, China, 710049

1 2

wrchen@zzu.edu.cn; lihua@zzu.edu.cn; 653852518@qq.com

Received 3 October 2013; Revised 29 January 2014; Accepted 13 February 2014; Published 17 April 2014 © 2014 Biological and Chemical Publishing

Abstract The solubility of thiourea in triglycol + water mixture has been determined with the mass fraction of triglycol (ω) being 0.63, 0.72, 0.82, and 0.91. The experimental data have been correlated with the modified Apelblat equation. The dissolution enthalpy and dissolution entropy have been calculated from the experimental data. The mutual interactions between solvent and solute have been discussed in brief.

Key words: Solubility; Dissolution Enthalpy; Dissolution Entropy; Thiourea; Triglycol Solution

Introduction Thiourea is a very important pharmaceutical intermediate and chemical material, which is widely used in synthetizing sulfnamides, dyestuff, resin and other substances. During the producing process, it’s significant to obtain the solubility and thermodynamic properties of thiourea in triglycol + water solution. In the literature [1], the solubility of thiourea in triglycol + water had been determined from 292.05 to 357.75 K by the synthetic method.

Based on the solubilities of thiourea in triglycol + water mixtures with the mass fraction of triglycol being 0.63, 0.72, 0.82 and 0.91 [2], the solubility data were correlated by the modified Apelblat equation and the dissolution enthalpy and dissolution entropy had been calculated, and the solubilities correlated by the modified Apelblat equation showed good agreement with the experimental data.

Experimental Section Materials Thiourea, triglycol, and water were of analytical grade, and all obtained from Shanghai Chemical Reagent Co. and had the mass fraction purities of 0.995. Deionized water was used.

Solubility Measurement The solubilities of thiourea in triglycol + water were measured by a synthetic method at atmospheric pressure which can be seen in the previous article [2]. The solubility of thiourea expressed by the mole fraction is shown as follows [3]. x

m1 / M 1 (1) m1 / M 1  m2 / M 2  m3 / M 3

Where m1 represents the mass of solute, m2 and m3 represent the mass of solvents, respectively. M1 is the molecular weight of solute and M2, M3 are the molecular weights of solvents, respectively.

1= thiourea, 2= triglycol, 3=water Test of Apparatus To prove the feasibility and the uncertainty of the measurement, the solubility of NaCl in water was measured and

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Physical Chemistry Communications, Volume 1 Issue 1, April 2014 www.bacpl.org/j/pcc

compared with the values reported in the literature [4]. The experimental data agreed with the reported values with a mean relative deviation of 0.18 % and 2.5 %, respectively. The measured values are listed in Table 1.

TABLE 1 SOLUBILITY OF NACL IN 100g WATER

T/K x x[4] 100 RD 293.15 0.0996 0.0998 ‐0.20 313.15 0.1015 0.1013 0.20 333.15 0.1033 0.1030 0.29 353.15 0.1061 0.1058 0.28 373.15 0.1090 0.1092 ‐0.18

Result and Discussion The measured solubilities of thiourea in triglycol+ water solution at different temperatures can be seen in the Table 2.

TABLE 2 MOLE FRACTION SOLUBILITIES OF THIOUREA IN TRIGLYCOL + WATER MIXTURES

T/K x xc 102RD T/K x xc 102RD ω=0.63 303.45

0.1449

0.1423

‐1.79

322.75

0.1883

0.1903

307.65

0.1515

0.1542

‐1.78

326.05

0.2002

0.1999

‐1.06 0.15

312.15

0.1605

0.1660

‐3.43

329.55

0.2086

0.2113

‐1.29

315.85

0.1675

0.1734

‐3.52

334.25

0.2229

0.2286

‐2.56

318.75

0.1780

0.1800

‐1.12

338.45

0.2322

0.2365

‐1.85

293.15

0.1686

0.1705

‐1.13

318.85

0.2316

0.2266

2.16

296.15

0.1792

0.1837

‐2.51

321.15

0.2387

0.2331

2.35

300.25

0.1885

0.1888

‐0.16

323.75

0.2435

0.2409

1.07

304.65

0.1989

0.1957

1.61

327.25

0.2547

0.2524

0.90

309.25

0.2057

0.2041

0.78

330.15

0.2621

0.2628

‐0.27

313.65

0.217

0.2136

1.7

332.85

0.2682

0.2733

‐1.90

316.45

0.2244

0.2203

1.83

335.95

0.2744

0.2863

‐4.34

ω=0.72

ω=0.82 292.05

0.2222

0.2315

‐4.18

320.35

0.2824

0.2782

1.48

292.25

0.2226

0.2317

‐4.09

321.65

0.2851

0.2811

1.4

292.85

0.2232

0.2324

‐4.12

324.35

0.2924

0.2873

1.74

297.25

0.2344

0.2378

‐1.45

327.55

0.2987

0.2951

1.21

301.35

0.2399

0.2435

‐1.5

331.15

0.3044

0.3044

0

301.55

0.2459

0.2438

0.85

332.85

0.3085

0.309

‐0.16

305.75

0.2527

0.2503

0.95

336.65

0.3173

0.3198

‐0.79

305.95

0.2552

0.2507

1.76

339.95

0.3254

0.3297

‐1.32

310.55

0.2651

0.2586

2.45

342.55

0.3330

0.3379

‐1.47

311.65

0.2642

0.2606

1.36

345.65

0.3414

0.3481

‐1.96

314.85

0.2726

0.267

2.05

348.65

0.3525

0.3585

‐1.7

319.15

0.2774

0.2756

0.65

ω=0.91

309.75

0.3248

0.3367

‐3.66

336.05

0.3714

0.3748

‐0.92

311.25

0.3313

0.3381

‐2.05

339.05

0.3778

0.381

‐0.85

313.15

0.3345

0.3399

‐1.61

342.25

0.3843

0.388

‐0.96

315.95

0.3372

0.343

‐1.72

345.65

0.3910

0.396

‐1.28

319.35

0.3418

0.3472

‐1.58

348.15

0.3947

0.4022

‐1.9

321.55

0.3472

0.3502

‐0.86

351.75

0.4045

0.4117

‐1.78

324.85

0.3497

0.355

‐1.52

354.35

0.4098

0.4188

‐2.2

327.85

0.3547

0.3598

‐1.44

357.75

0.4166

0.4287

‐2.9

332.05

0.3637

0.3671

‐0.93

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www.bacpl.org/j/pcc Physical Chemistry Communications, Volume 1 Issue 1, April 2014

The temperature dependence of thiourea in triglycol + water mixtures is described by the modified Apelblat equation [5, 6]. ln x  A 

B  C ln T T

(2)

Where x is the mole fraction solubility of thiourea, T is the absolute temperature, and A, B, C are the model parameters, which can be obtained from optimization and fitting. The values are listed in Table 3.

TABLE 3 PARAMETERS OF EQUATION 2 FOR THIOUREA IN TRIGLYCOL + WATER MIXTURES

ω A B C R2 103RMSD 102RAD 0.63 ‐255.33 10798.39 38.12 0.983 3.807 2.882 0.72 ‐196.62 8161.00 29.41 0.971 3.604 2.035 0.82 ‐92.98 3648.85 13.92 0.982 2.227 1.401 0.91 ‐89.99 3872.20 13.32 0.992 3.848 1.657

The root‐mean‐square‐deviation (RMSD), relative deviation (RD), and relative average deviation (RAD) are calculated respectively according to the previous reference [2]. The model parameters, RAD, and RMSD are listed in Table 3. The relative deviations between experimental values and calculated values are listed in Table 2. From Table 2, it can be seen that the experimental data show good agreement with the calculated data. And the relative average deviations of thiourea in triglycol + water mixtures are 2.882%, 2.035%, 1.401%, and 1.657% respectively, which indicates that the Apelblat equation is fit to correlate the solubility data of thiourea in triglycol + water mixtures.

Thermodynamic functions related with solubility are mainly dissolution enthalpy and dissolution entropy, namely ΔH and ΔS, which can be obtained though a series of equations. According to a pseudochemical reaction process [7], the dissolution process of solid S in liquid W, can be expressed as S+W=SW; the relationship between its dissolution equilibrium and activities can be expressed as: Ki 

ai (3) as  aw

Where ai stands for the activity of thiourea in the solution, as and aw represent the activities of pure solid S and pure liquid W, respectively. Because of the relatively small solubility of thiourea in solvent, it is believed that a s and a w almost remains constant in the experimental range, and each is considered to be a constant.

Meanwhile, the activity ai and the mole fraction xi are related by the Equation (4), which is shown below.

Therefore Equation (3) can be written as Equation (5) as below. ai   i  xi (4) Ki 

 i  xi (5) as  aw

Where γi is the activity coefficient of thiourea, and xi is the mole fraction of thiourea in the solution.

By logarithmic treatment, Equation (5) can be changed into: ln Ki  ln xi  J (6)

Where J=lnγi‐ln (as *aw), which is a constant independent off temperature.

On the basis of Gibbs equation and the modified Van’t Hoff method [8], the equation for calculating molar enthalpies of dissolution ΔsolH can be obtained:  sol H   R 

d ln K i dT 1

(7)

That is to say,

 sol H   R 

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d ln xi dT 1 (8)

Physical Chemistry Communications, Volume 1 Issue 1, April 2014 www.bacpl.org/j/pcc

Then Equation (2) is used to obtain the derivation and then substituted into Equation (8), thus Equation (9) is given below.  sol H  R  T  (C 

B ) (9) T

According to the fundamental thermodynamic relation [9], the equation for calculating the molar entropy of dissolution ΔsolS can be obtained accordingly:  sol S  R  (C 

B ) (10) T

R is the molar gas constant, whose value is 8.314 J∙mol‐1∙K‐1; According to the parameters of modified Apelblat equation listed in Table 3, ΔsolH and ΔsolS can be calculated by Equation (9) and Equation (10), which is listed in Table 4.

TABLE 4 ΔSOLH (KJ MOL‐1) AND ΔSOLS (J MOL‐1 K‐1) FOR THIOUREA IN TRIGLYCOL SOLVENT WITH THE MASS FRACTION OF THIOUREA BEING 0.63, 0.72. 0.82,

0.91 AND 1.00 RESPECTIVELY T/K

ΔsolH (kJ mol‐1)

ΔsolS (J mol‐1 K‐1)

T/K

ΔsolH (kJ mol‐1)

ΔsolS (J mol‐1 K‐1)

303.45

6.394

21.073

307.65

322.75

12.511

38.764

7.726

25.112

326.05

13.557

41.580

312.15

9.152

29.319

329.55

14.666

44.504

315.85

10.324

32.688

334.25

16.156

48.335

318.75

11.243

35.274

338.45

17.487

51.668

ω=0.63

ω=0.72 293.15

3.829

13.061

318.85

10.113

31.717

296.15

4.562

15.405

321.15

10.675

33.241

300.25

5.565

18.534

323.75

11.311

34.938

304.65

6.641

21.798

327.25

12.167

37.179

309.25

7.766

25.111

330.15

12.876

39.000

313.65

8.841

28.189

332.85

13.536

40.667

316.45

9.526

30.103

335.95

14.294

42.548

ω=0.82 292.05

3.463

11.856

320.35

6.738

21.033

292.25

3.486

11.927

321.65

6.888

21.416

292.85

3.555

12.140

324.35

7.201

22.201

297.25

4.064

13.674

327.55

7.571

23.114

301.35

4.539

15.062

331.15

7.988

24.121

301.55

4.562

15.129

332.85

8.184

24.589

305.75

5.048

16.511

336.65

8.624

25.618

305.95

5.071

16.576

339.95

9.006

26.493

310.55

5.604

18.044

342.55

9.307

27.170

311.65

5.731

18.389

345.65

9.666

27.964

314.85

6.101

19.378

348.65

10.013

28.719

319.15

6.599

20.677

ω=0.91

309.75

2.109

6.809

336.05

5.022

14.943

311.25

2.275

7.310

339.05

5.354

15.790

313.15

2.486

7.937

342.25

5.708

16.678

315.95

2.796

8.848

345.65

6.085

17.604

319.35

3.172

9.933

348.15

6.362

18.272

321.55

3.416

10.623

351.75

6.760

19.219

324.85

3.781

11.640

354.35

7.048

19.890

327.85

4.113

12.547

357.75

7.425

20.754

332.05

4.579

13.789

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It can be seen from Table 4 that at the same temperature, ΔsolH and ΔsolS both decrease when the mass fraction of triglycol (ω) increases, ΔsolH and ΔsolS increase when the temperature increases and mass fraction of triglycol (ω) keeps stable; and the process of thiourea dissolving in triglycol + water mixtures during the temperature range is endothermic, ΔsolH＞0. The endothermic effect happens mainly because the interactions between thiourea and the solvent are more powerful than those between the solvent molecules. Meanwhile, ΔsolS for the process is positive, which reveals that it is irreversible processes.

Conclusion The solubilities of thiourea in triglycol solution were measured, and the experimental data were correlated with the Apelblat equation, also the dissolution enthalpies ΔsolH and dissolution entropies ΔsolS were calculated. The overall RMSD is 1.349×10‐2, indicating that the calculated data show good agreement with the experimental data. The positive ΔsolH and ΔsolS revealed the process is endothermic and entropy‐driven. The experimental solubilities and correlation equation in this work can be used as essential and basic data for the preparation of thiourea.

Literature Cited [1]

H. Li, G. Feng, G.Q. Hu, L. Zhao, Y. D. Zhang. “Measurement and Correlation for Solubility of Thiourea in Triglycol + Water at Temperatures from (292.05 to 357.75) K.” J. Chem. Eng. Data. 54(2009): 2100‐2102. doi: 10.1021/je900040n.

[2]

H. Li, X. S. Chen, and F. Guo, “Enthalpy of solution for thiourea in triglycol and water.” Russian Journal of Physical Chemistry. 84(2010): 2259‐2261. doi: 10.1134/S0036024410130091.

[3]

X. H. Shi, C. R. Zhou, Y. G. Gao, and X. Z. Chen.“Measurement and Correlation for Solubility of (S)‐(+)‐ 2,2‐Dimethylcyclopropane Carbox Amide in Different Solvents.”Chin. J. Chem. Eng., 14(2006): 547‐550.

[4]

C. M. Xue and Y. Fan, Common Chemistry Handbook, Geophysics Press, Peking, 1997.

[5]

A. Apelblat, E Manzurola, “Solubility of Ascorbic, 2‐Furancar‐boxylic, Glutaric, Pimelic, Salicylic, and o‐Phthalic Acids in Water from 279.15 to 342.15 K, and Apparent Molar Volumes of Ascorbic, Glutaric, and Pimelic Acids in Water at 298.15 K.” J. Chem. Thermodyn. 21(1989): 1005–1008.

[6]

A. Apelblat, E. Manzurola, “Solubilities of o‐Acetylsalicylic, 4‐Aminosalicylic, 3, 5‐Dinitrosalicylic, and p‐Toluic Acid, and Magnesium‐DLaspartatein Water from T = (278 to 348) K.” J. Chem. Thermodyn., 31(1999): 85‐91.

[7]

F. A. Wang, Molecular Thermodynamics and Chromatographic Retention, Meteorology Press: Beijing, 2001.

[8]

D. Bourgois, D. Thomas, J. L. Fanlo, and J. Vanderschuren, J. Chem. Eng Data, 2006, 51,1212.

[9]

J. M. Prausnitz, R. N. Lichtenthaler, E. G. Azevedo, Molecular Thermodynamics of Fluid‐Phase Equilibria, 3rd ed Prentice Hall PTR, Upper Saddle River, New Jersey, 1999.

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